Process and product for covering a metallic article with an unworkable alloy



Patented Aug. 2, 1932.

UNITED STATES PATENT OFFICE WILLIAIvI J. WRIGHTON, 0F SOUTHBRIIDGE, MASSACHUSETTS, ASSIGNOB TO AMERICAN OPTICAL COMPANY, OFSOUTHBRIDGE, MIASSACHUSETTS, A VOLUNTARY ASSOCIA- 'IION OF MASSACHUSETTS rnocnss AND rnonnor FOB oovEnInGA METALLIC ARTICLE WITH AN UNWORKABLE ALLOY No Drawing.

This invention relates to .a process ofcovering a metallic article with an alloy comprised of the intermingling of the base and cover, and has particular reference to covering a metallic article with an unworkable alloy possessing certain desired characteristics and to the product produced thereby.

The principal object of the invention is to provide an improved process and product for covering a metallic article with an alloy that is brittle and unworkable, which covering shall possess advantages of color and antitarnish characteristics.

Another object of the invention is to provide such an improved process and product that will permit of covering a metal article with a metal that would have a grain if worked, which metal covering possesses the desired characteristics of color and anti-tarnish. 7

Another object of the invention is to provide improved means whereby tarnish or discoloration of certain metal articles may be reduced or avoided.

Another object .of the invention is to provide an improved process and product whereby a finished and completed article may be covered with a metallic covering which will not tarnish and which has the desired color and which also may beof a metal that would be otherwise unworkable.

7 Another obj ectof the invention is to provide an improved process and product where p by a metal article covered with another metal will possess the characteristics of an alloy comprising the intermingling of the ingredicuts of the cover and'the base.

Another object of the invention is to provide a finish for a metallic article that will be impervious to the action of strong acids, tarnish, grainv and other defects that mar the finish.

Other objects and advantages of the invention willbecome apparent from the following description and it will be understood that many changes may be made in the steps of the process and the substances named without departing from the spirit of the invention as expressed in the accompanying claims. I, therefore, do not wish to be limited to the Application filed September 11,- 1928. Serial No. 305,335.

exact details described, as the preferred forms and order of operations have been given by way of illustration only.

It has been found from experience in the manufacture of metallic articles, particularly articles in the nature of jewelry .or precious metal, that they are subject to tarnish, oxidation and other defects that destroy the surface finish and thus make the articles undesirable for the purpose for which they were created.

It has also been found from experience in the manufacturing arts that there are many metals that possess the, desired characteristics of color and are free from liability to ready oxidation or tarnish, but are unworkable and unadaptable to the manufacturing processes due mainly to the fact that they are too brittle and will crack or break when worked or bent and also that they possess a grain which becomes very apparent when the article is stretched or drawn in the working operations.

It is, therefore, one of the prime objects of my invention to produce a finished metallic article of the desired shape and configuration and thereafter cover it with a finished coating of a metal which could not have been worked to produce the article due to its brittleness or its tendency to Show a grain, yet which metal covering possesses the desired color and freedom from liability to oxidize, tarnish or to be affected by strong acids, etc.

The wide application of this process will become clear from the following description and from the examples hereinafter mentioned, but as a detailed account .of each of its different phases is unnecessary I will confine the description of the process to an alloy of say white gold and tin, this producing an article of widespread demand and use, but it will be clear that the teachings of this process may be applied to many combina tions of base metals and covering metals therefor.

lVh-ite gold is well known for its pleasing luster and color, being a metal which is associated in the arts with the appearance of the more precious and .expensive metal, platinum. .Hitherto the finish or luster of white gold has been quickly dimmed and a tendency to tarnish quickly has been experienced especially upon exposure of the article so made to certain chemical elements in the atmosphere, especially sulphur. Strong acids also have an undue eliect upon the finish of white gold. It has been found from experience that the manufacturers of white gold articles have to take special care in packing these goods in envelopes anu containers to prevent their tarnishing and discoloration, which is due primarily to the presence of sulphur either in the paper forming the container or in the inks which are sed to print the said envelopes and containers. Due to its beauty and attractive qualities white gold is greatly favored, but its tendency to tarnish has, of course, a tendency to reduce the demand for such an article, and it is believed that unless a cure is found the demand for this metal in the arts will eventually be destroyed. It will, therefore, be seen that if these disadvantages are overcome the popularity and demand for white gold will increase. Attempts have been made to overcome this defeet but so far as I am aware without practical success. In the case of white gold alloys it has been found almost impossible to produce a finished article free from cracks and a noticeable grain as those alloys possessing a freedom from tarnish are extremely brittle and have a grain which tends to develop when the metal is worked.

This invention is based on the principle that it is not necessary to make an alloy before working the article into finished shape. An alloy of tin and white gold, for instance, can be made after the base of white gold has been wrought into filial shape and all the tooling completed. his is possible because the melting point of tin is much lower than that of white gold. This process, therefore, is essentially one of making an alloy on the article itself after the article has been worked to shape and completed.

In describing the preferred method of using the process it will be understood that the two metals employed for illustration pur poses are not to constitute the limit of the process and ingredients many metals of suitable quality may be alloyed with equal facility and give similar satisfactory resuits.

One commercial alloy of white gold consists of fifty parts of the combination of sixty parts copper, twenty-two parts nickel and eighteen parts zinc alloyed with fifty parts of pure gold by weight. This alloy is formed into the desired shape, such as lens rims for eyeglasses or any other desired article. After the article has been finished to shape in any well known method of working it is finally polished as on a buffing wheel, or by rattling. The article is then placed in an NA P O lOH O. This bath is heated to 60 degrees centigrade. The electro-plated article is then placed in a furnace, being covered with powdered charcoal andsubmittedto the action of heat at a temperature of from 240 to 250 degrees centigrade, whereby the electro-plate covering of the tin will melt and alloy with the white gold base. It will be noted here that the melting temperature of tin is about 230 degrees centigrade. After the covering has thus been melted so as to alloy and join with the base of white gold the article is allowed to cool and it is then polished on a bufiing wheel or otherwise finished by well known methods in the prior art, when it will be found to have a color and luster superior to the original white gold base and will be free from the action of acids, particularly nitric acid and from a tendency to tarnish. The color of the alloy coating is a clear blue white, which is very desirable and much preferable to the colors obtained in white gold alloys hitherto produced. It will be noted that an alloy of tin and white gold is very brittle and produces a grain when worked and, therefore, an article could not be made and worked of this alloy, yet if the alloy is applied by the process herein described the finished article may be covered with a beautiful finished coating of this desirable alloy.

An important feature of this invention resides in the fact that a metal both tarnishable and workable can be alloyed with another metal also tarnishable and workable and the product of this combination is an alloy which is non-tarnishable and unworkable.

The alloy of tin and white gold is of a very brittle nature and any attempt at working it results in the appearance of a grain and in cracking or breaking. The alloy is also of a non-tarnishable nature and the atmospheric chemicals, such as sulphur and its constituents, do not affect the surface in any way. As the article is finished to desired shape before the alloy process the unworkability does not affect the final appearance nor hinder the process of manufacture. The non-tarnishability, however, is greatly to be desired and is a feature of prime importance to the art.

While I have described my process for producing a white gold article with the alloy covering of tin, a similar process may be used to make other alloys; for instance, an alloy of precious metal on a base metal core or an alloy of one precious metal on a core of another precious metal as long as the melting point of the cover is lower than the base core.

From the foregoing description it will be seen that by my new and novel process I have produced an article of a material having the desired characteristics of color and anti-tarnish, yet which material could not have been used for making the article itself due to its inability to be worked, bent and drawn for the reasons stated above, and it will be seen that the product of my process is in itself a new and useful article of manufacture. The invention described provides a simple, efiicient and economical means of producing the desired results and the advantages of the invention.

Having described my invention, 1 claim:

1. An article of the characterdescribed comprising a shaped article of fifty parts by weight of gold combined with fifty parts of an alloy consisting of sixty parts of copper, twenty-two of nickel and eighteen of zinc having a covering of tin alloyed therewith.

2-. An article of the character described composed of a tarnishable gold base and a coating of tin thereover, said coating being alloyed to the gold and rendering said article non-tarnishable.

3. An article of the character described composed of a tarnishable gold alloy base and a coating of tin thereover said coating being alloyed to the gold alloy base and rendering said article non-tarnishable.

WILLIAM J. WVRIGHTON. 

